flow_dissector: support L2 GRE

Add support for L2 GRE tunnels, so that RPS can be more effective.
Signed-off-by: NMichael Dalton <mwdalton@google.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -119,6 +119,17 @@ bool skb_flow_dissect(const struct sk_buff *skb, struct flow_keys *flow)
 				nhoff += 4;
 			if (hdr->flags & GRE_SEQ)
 				nhoff += 4;
+			if (proto == htons(ETH_P_TEB)) {
+				const struct ethhdr *eth;
+				struct ethhdr _eth;
+
+				eth = skb_header_pointer(skb, nhoff,
+							 sizeof(_eth), &_eth);
+				if (!eth)
+					return false;
+				proto = eth->h_proto;
+				nhoff += sizeof(*eth);
+			}
 			goto again;
 		}
 		break;